Reading PDFs is the biggest case. PDFs do not (typically) dynamically reflow in a way that's usable and generally suck to read on a small screen as a result. Source: read a lot of PDFs on mobile.

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ashirviskas 4 days ago | parent [-]

But most books are probably not PDFs?

	▲	packetlost 4 days ago \| parent [-]
		Most? Idk maybe. Most papers are. Most TTRPG books I've encountered are. Textbooks are often PDFs, not EPUBs. Nah, I'd say most digital books are probably PDFs.